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Going to Baja on GMZ tires.

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7.3K views 23 replies 9 participants last post by  Desertwheeler  
N
#1 · (Edited)
Going to Baja on GMZ tires. (Post Trip Upates)

I've been doing a bunch of tire research as I'm doing another Baja trip. There are allot of new tires out there and several are really good. But what I need is a full all terrain tire. In Baja we will be on every type of surface you can think of. Graded road, dirt trails, rock, sand wash, silt, beach sand and we will even be driving down the asphalt highway. While tire wear is important, too hard of a compound or stiff tire, will not perform as well in the soft stuff. Too soft and we will wear them out in 500 miles and tear them up on the rocks. A square edge tread can have to much bite and can rut track, especially in a lighter vehicle like a UTV. This is why you see rounded tread pattern tires used on lighter buggy race cars. We also looked at a steel belted tire, but I just dont think such a stiff and heavy tire is worth the trade off. If I wanted that weight I would rather put that weight in a taller tire, then a smaller heavier tire.

So I looked at the GMZ Race Products tires. GMZ does not have the marketing or web presents that some other tire brands do. They seem to be under the radar in many ways. But after speaking directly with one owner of GMZ, I felt they had the best tire for what we were doing. Try calling some of the other popular brands and see how far you get. Ask for engineering or tech? I did and got nowhere!

GMZ is 3 partners and all three have not only a racing background, but they have all worked in the tire & wheel industry before starting GMZ. GMZ actually designs their own tires & wheels. Many of the other brands contract out to have their tires designed and manufactured by someone else. Part of GMZ is overseas and is in the factory's that they have contracted to manufacture their tires.

GMZ has the Cutthroat tire which is a 28X10-14 inch tire. And they have the Kahuna tire which is offered in a 30X10-14 and now a 15". For our application (XP4 900's) we felt the 30inch Kahuna was to much tire, as we have stock clutching & axles. Plus I can relate to the tread of the Cutthroat, as it is very much like the Yokohama Super Digger 3, which is the most winning #1 limited buggy tire in Baja. The Yokohama is also a nylon corded radial tire, not steel belted to keep it light & pliable.


Yokohama Super Digger 3 (Rounded tread)
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GMZ Cutthroat 28x10-14
Specs: 6 ply radial, D.O.T approved, weight 31 lbs.
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GMZ Kahuna 30X10-14
Specs: 8 ply radial, D.O.T approved, weight 33 lbs.
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The Cutthroat measured right at 28 inches mounted with 10lbs of air in the tire.
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So for this trip we bought 10 GMZ Cutthroat tires. I weighed 4 of the 10 on a digital warehouse scale and all 4 weighed between 30.7 & 31.1 lbs. (Sorry no pictures.) This Baja trip is going to be in the 500+ mile range and we will be able to see real results and not just opinion about the GMZ Cutthroat. I expect to see tire wear. If I did not I would say we are on way to hard of a tire compound. I want 50K mileage out of my truck tires, but not my recreational or race vehicle tires. We would kill a set of Yokohama race tires on the race car in 500 miles. I expect the GMZ to wear better as they seem to have a bit harder compound, and we will not be running race speed all day over all the terrain we will face.

When we get back I will share our trip and post results of the GMZ Cutthroat tire. I will either have great things to say, or I will be telling you about the wrong tire for our trip.

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BTW; the most winning UTV tire in Baja & BITD right now is the ITP Ultracross R. BFG just released what is expected to be the next King of UTV tires in Baja the KR2. What do these two tires (which were produced after the GMZ Cutthroat) have in common with the GMZ Cutthroat? Both are nylon cord radials and are designed with a rounded edge tread. But neither are DOT approved like the GMZ Cutthroat.

BFG builds the most winning tires in Baja period, and all have been steel belted until they built this new KR2 30" UTV & 35" class 10 tire.Why? Because they understand a lighter tire is needed for limited power vehicles. General Tire builds the Grabbler Red Label off-road tire, which they too built with Nylon cord and not steel belts and is very popular with the truck & high HP buggy classes. Just something to think about!

http://gmzraceproducts.com
 
N
#3 · (Edited)
We liked the 8 ply 30" Kahuna and I think for a XP1000 its the perfect tire, with no mods needed. But for the XP4 900 I felt I would have to do to many mods to make it perfect. For example I think the stock axles might be an issue with that much rotating mass? I could be wrong? But did not want to chance it with doing a 500-600 mile Baja trip. And buying new axles for two UTV's on top of wheels & tires was not an option at this time.

Also we would have to re-clutch the both UTV's and that was something we did not want to have to do, as we also run the 27" Bighorn/GMZ Slasher tires when we run at Superstition/Plaster City and Gordon's Well. Going from the 27 to 28" should not effect our clutching that much if at all, but jumping to a 30" would clearly effect clutching. The Bighorn/Slasher style tire works really good in sand dunes, yet is still versatile on hard pack, unlike a paddle tire where your stuck in only dune mode. I know some don't have an issue with doing multiple clutch tunes for different riding or trips. But for me that is something I don't want to do, and was the biggest factor in not choosing to step up to the 30" Kahuna. Then we would have to cut & clearance the front fenders, which is no big deal, but it was one more thing to consider if we were to run the 30" Kahuna.

Last years Baja trip we did use the Bighorn tires and while they got the job done, we did have two punctures, and you could see that tire was just not designed to do what we did. It beat them up pretty good.

I will post results and my opinion of the GMZ Cutthroat when we get back from Baja next week. Plus I plan to try them on our first Superstition/Plaster City trip of the new season. I know the Cutthroat is more designed as a all terrain Baja type of tire, but it will be interesting to see how they do in the Superstition Sand. I know in the washes & hard pack around Superstition they will be great.

Thanks for asking.
 
N
#5 · (Edited)
Post Trip UPDATE

We did 580 miles over 3 days in Baja on the GMZ Cutthroat tires. The types of terrain or things we ran on were; Graded dirt roads, Rutted, whooped out Score Race course, Good & bad asphalt, Silt, Granite based dirt roads with 1 inch loose rock, Sand wash, boulders, small vegetation including cactus, barbed wire, red clay, beach sand, large beach rock and a first for me was Volcanic rock.

Now to the facts;
We had ZERO flats or punctures.

We started with 12lbs cold in the front tires, and 14lbs cold in the rear. These are good pressures, but what we found was that the tires would grow about 2.5lbs as they built up heat. So the rears were around 16.5 lbs with the fronts over 14lbs after about 1 hour of running. We planned to lower the pressures for day two.

Day two we checked all the tires first thing in the morning and we found that all the tires cold had lost about 1lbs per tire. This was found on all 8 tires on both RZR's. It was strange, yet consistent, so we knew it was not a leak. So fronts were 11 lbs & rears were 13lbs cold. Only thought is that all 10 tires were mounted and aired up using my compressor. Maybe my compressor has moisture in it and the condensation built up in the compressor and put in the tires, evaporated when the tires got hot. Once cooled they were now 1 lbs lower then when we started? We talked about trying Nitrogen in the future as Nitrogen is more consistent vs compressed air.

Now for tire wear;
I expected tire wear, as any tire that does not shows some wear after 580 off-road miles is going to be too hard of a tire compound and you will lose grip & performance IMO. Consider that in the Baja 500, running race speeds & conditions you should almost wear out a set of rear tires, if you were to run the full race without getting a flat or changing them. (For the record we were not running race speeds most of the time, and slowed for obstacles that you typically would not slow for in a race where tire spin would increase tire wear & possibly damage a tire.)

Here are factual specs of the REAR tire wear;
Brand new GMZ claims the tread to be 3/4 tall (.750 or 25/32)
I checked and per my digital calipers that the tread depth was .745, so that is damn close to 3/4 or 25/32 (.750). After running 580 Baja miles I measured the Rear tires and found they measured .656 which equals 21/32. So total wear was .0937 which would be 3/32 of tire were. That is a smidgen less then 1/8th inch of wear.

.750 new tire (3/4 or 25/32)
.656 used tire (21/32)
.09375 total wear (3/32) Just under 1/8 inch.

While just under 1/8 inch is noticeable, most of the visual wear looks to be as the square edge of the knobby tread is rounded off. Also I have found a few cuts and nicks in the actual tread of the rear tires, this too is common and was not a surprise. (The loose Granite and Volcanic rock are sharp and wheel spin will wear, cut and damage tires real quick if you dont manage your tires. In those places I tried to dial it back and conserve not only the tires but the equipment as a whole, as we have Zero support with us to get us back to our trailers hundreds of miles away.)

After 580 miles


I only found a few cuts, and this was one of the worst I found.



Now here is my Opinion;
If GMZ were to call me and ask what I would like to see as an improved Cutthroat? I would suggest they tighten up the tread. I measured and found some parts have just over 1 inch between tread knobby's. Keep the tread gap about 1/2. This would help in many places, as it would reduce puncturing the casing of the tire, reduce rounding off the edge of the tread, and reduce noise. Also between the larger areas of tread gap I would add small Stone Ejectors as you would not want rocks to stick between the tighter tread and cause stone drilling into the tire carcass. I think with the GMZ Kaunha they addressed many of these issues as the tread on the Kahuna looks to be tighter. Also the Cutthroat is being used in short course racing, so what is better for my type of use, might hurt the the performance in other types of use. If GMZ made a 28 inch Kahuna I would try it, as it might check off those box's I mentioned above.

Overall Myself and my Brother in Law were very, very impressed with the handling of the GMZ Cutthroat tire. The rounded tread worked really well in the rutted sections of race course we ran as it did not rut track, and the side wall tread allows you to pull out of the ruts easier then a square edge tire. Same with the small silt bed pockets we ran into. The extra ground clearance we got vs. the last time we ran the Bighorn tire was a noticeable improvement. I dont have allot of experience with other current brands of UTV tires, but the Cutthroat excelled over the Maxxis tire in every place, except for the sand dunes on some of the beaches. The Bighorn tread gives you a paddle effect, that a Baja All Terrain tire is not going to give you. Unlike the last trip on Bighorns we had Zero punctures with the Cutthroat tires. I highly suggest the GMZ Cutthroat if your looking for a 28 inch all terrain tire. Give Black Rhino a call as they are a GMZ dealer. We proved they are Baja tough!



 
#9 ·
I would buy these in a heartbeat if they made a 30, so its either the kahuna or the tensor. Can you tell anything about the sidewalls yet? It makes me nervous with the mongrels or stockers with the soft sides. Really don't want to spend all my play money on tires non stop
 
#11 ·
Great write up. I too continually research details of tires/wheels for my sxs as well as personal vehicles.

Tires are such an under utilized tool that can greatly effect your satisfaction with a vehicle. Even small air pressure adjustments can make a very noticeable change.

I have looked a kahuna's for awhile. I have been concerned about their tread Separation in mud performance situations. I DON'T "mud ride" but on the east coast it's unavoidable at times. Sometimes you need the grip to pull out of a creek bank or cross rutted sections.

In the past I have used:

GBC Grim Reaper-
Unbelievable snow and slick mud traction, poor side wall performance for me. (When I say slick mud I don't mean 3 feet deep, just mud caused my rain or run off)

GBC Mongrel -
Great all around tire, ride is good, asphalt performance is great. Side wall is in the weaker side, very poor in clay or heavy mud.

Bajacross-
Tough tire, not the smoothest ride, did everything ok.

Bighorn-
We all know +/-

STI Roctane-
Tough as nails, but didn't ride the best.

Currently I'm building a 2016 XP4 1000. Just started quite an extensive build. I plan to do a build thread once cage arrives. The only decision I have not made is tires and beadlocks.

Out of all tires I have liked the ride of the Mongrel the best, and overall performance, but we all know if you find yourself in mud you might as well get the winch. Snow performance is ok with the Mongrel.

I have been leaning heavily towards the Pro-Armor crawler or Hammer, but your take on the rounded edge of the tire and DOT rating has me taking a harder look at the Kahuna's.


Crawler

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Hammer

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I live in West Virginia which offers some amazing riding. However I have raced Baja on a Big Horn in my ATV days.

Anyone have experience with the Kahuna on the east coast or in mud?


Soon to be in a million pieces!

Image
 
#14 ·
I'm considering these tires as well when my mongrels wear out, which isn't too far away. How was the balance on these tires? I'm assuming you were on a high speed road now and then at least. Did they balance fine or need spin balanced? And the wear is definitely noticeable which is one of the huge problems I have with the mongrels. I do like the looks of the cutthroats and the fact that they measure out to an actual 28", again unlike the 28" mongrels. Thanks for the info.
 
N
#15 · (Edited)
We mounted all 10 tires ourselves and we did not balance them at all. So I cant tell you definitively if their is any minor balancing issues. But with that said neither XP4 had or felt any issues with the tires in regards to balance.

Yes we did do some higher speed roads, which included asphalt, smooth WET beach sand & graded road. We did between 50-60 mph on the asphalt, and in one picture on the beach you can see we are doing 60mph. Then you throw in the soft sand washes, larger rock gravel and rutted roads, cobble stone beaches, silt beds, and volcanic rock. These are all the types of terrain we road on this last Baja trip. Click the link to the Baja trip. You will get to read about the trip and see all the sites and terrain we drove over. I posted a ton of pictures!
http://www.rzrforums.net/general-rzr-discussion/181342-2015-baja-adventure-trip-report.html

I will say on the asphalt roads, like in town when running slower or slowing to a stop light or sign, you could feel a bit of a vibration, due to tread lug spacing. Not an out or round issue, just the lug spacing made it a bit rougher at slow or stopping speeds only on the asphalt. The Bighorns did it too, but for some reason I noticed it more with the Cutthroats. It could have been because I was really trying to study the tire, as I wanted to give as honest evaluation as possible.

As I mention in my original "Post Trip Tire Evaluation", if I could re-design or was asked by GMZ what to change, it would be to tighten up the tread and add some stone ejectors in the areas where rocks could get stuck due to the tighter tread and cause stone drilling.
 
N
#18 ·
Glad to hear you chose a tire. I hope your as happy with the Kahuna as I am with the Cutthroat. If they made a 28 inch Kahuna I would have probably tried them too. Where did you buy them from? I got mine threw Black Rhino, but saw some awesome deals at the Sand Show. Chaperral had smoking deals on both the Kahuna & Cutthroat tire.
 
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