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Old 16th April 2008, 16:30   #1
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Default Effect of bigger tyres on an offroader

hi ,

I am planning to fit 9.00 x 16" NDMS tires on a SWB Jeep. If you are wondering what tire this is, it is the one fitted on JCBs front wheels.

Wondering what kind of issues/performance I can expect. I could think of the following issues :

1. Need wider rims ( 6 to 6.5" width instead of the present 4.5")to fit the tires.
2. Need to increase clearance height to compensate for the bigger tires.
3. Better fuel efficiency due to large diameter of tire ?
4. Poor fuel efficiency due to heavier tires/rims ?
5. Poor braking due to bigger tires - Need to go for disc brakes.
6. Poor Pickup... Will the vehicle atleast move normally?

I am not in a position to fit the tires and then check out the performance. It would be better to at least in theory analyse it and then go for it...( if it makes sense...)

BTW it would have a Peugeot DI diesel engine, 5 speed gear box, 4x4, Free wheeling hubs, etc.

Regards
Anand
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Old 16th April 2008, 17:27   #2
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Quote:
Originally Posted by aandu View Post
hi ,

I am planning to fit 9.00 x 16" NDMS tires on a SWB Jeep. ...

1. Need wider rims ( 6 to 6.5" width instead of the present 4.5")to fit the tires.
2. Need to increase clearance height to compensate for the bigger tires.
3. Better fuel efficiency due to large diameter of tire ?
4. Poor fuel efficiency due to heavier tires/rims ?
5. Poor braking due to bigger tires - Need to go for disc brakes.
6. Poor Pickup... Will the vehicle atleast move normally?

...
1. & 2. need to be done for sure. While doing 2., steering control will also get affected
6. I guess the good low-end torque of diesels will negate this effect.


OT : have you got the tyre prices? and which brand?
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Old 16th April 2008, 17:37   #3
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Your tyre choice would depend a great deal on what kind of driving you would do.

Overall I would recommend radials, as they are lighter and provide superior traction. Be it on road or off, this matters. You also get better mileage.

Secondly the tread pattern choice should depend on how often you go offroad. You have highway treads, all terrain, and serious offroad treads. If your vehicle use is a combination the all terrain tyres are great.

On deciding the size, while broader the better, there are limitations as you end up loading the steering, increased weight affects handling, and your wheel well restricts size useable(affects turning radious too). For a Jeep suggest you cut off at 235/70's as anything bigger would feel cumbersome

PS: The OE nylons off my Tata 207 felt like lead compared to the All Terrain Landcruiser radials I fit. The ride improved dramatically and so did the steering feel and grip.

Last edited by DKG : 16th April 2008 at 17:40.
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Old 16th April 2008, 17:51   #4
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Also be wary about the speed rating of the JCB front tires. Some tires are not designed to go fast. JCB tire, based on it's application, i'm sure is not meant for highway speeds.
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Old 16th April 2008, 18:09   #5
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I got 225's for my Jeep and wouldn't recommend anything wider than that. In fact, this size itself may be a little overkill for the kind of power (or lack of) that the diesels make.
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Old 16th April 2008, 18:13   #6
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Quote:
Originally Posted by Sankar View Post
Also be wary about the speed rating of the JCB front tires. Some tires are not designed to go fast...
this is a very valid point
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Old 16th April 2008, 20:57   #7
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9.00x16 translates to a 230/100 R16 tyre in our terms. For a Jeep this is going to be too wide, too tall & certainly not appropriate unless you have an engine putting out some serious power.

As for your questions, my answers are below:

1. Yes, minimum 6J, 6.5J recommended.
2. Yes, big time increase in wheel arch clearance required.
3. Nope, poorer fuel efficiency due to much wider contact patch & a lot more unsprung weight.
4. Yes, explained above.
5. Could be but this is a debatable issue. Also depends on the quality & construction of the tyre.
6. No it will not. It will move slowly & the figures on the stock gauges will be all skewed due to the bigger tyres. Plus the wider contact patch of the tyres coupled with the increased of the bigger tyres & rims will mean that the accelaration will be hurt big time.

I would suggest drop this idea since being off a JCB these tyres won't be suited for road use either. Get some nice 215/75 R15 radial, they'll be much better for your usage & more appropriate given the kind of power your vehicle has. Also, under normal circumstances they'll be much cheaper than the JCB's tyres.
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Old 16th April 2008, 23:54   #8
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Quote:
Originally Posted by aandu View Post
hi ,

I am planning to fit 9.00 x 16" NDMS tires on a SWB Jeep. If you are wondering what tire this is, it is the one fitted on JCBs front wheels.

Wondering what kind of issues/performance I can expect. I could think of the following issues :
You will definitely have much stronger arms after a few months of using your jeep.

Quote:
Originally Posted by GTO View Post
I got 225's for my Jeep and wouldn't recommend anything wider than that. In fact, this size itself may be a little overkill for the kind of power (or lack of) that the diesels make.
What are the full specs of the tire? I saw 225 only on the good year web-site.

Anand,

You haven't mentioned what kind of jeep you have. If it is the older CJs or pre 2004 MM540s the only rims that fit the same PCD are:

1. Gypsy 15 inch rims (5.5 inches)
2. Army MM540 (not sure how wide)
3. The OEM rims (4.5 inches wide).

I am figuring out what to do as I want to go to wider tires but don't want to drop to a 15 inch rim so the gypsy rim is ruled out. I am a bit concerned about putting wide tires on the standard 4.5 inch wide 16inch rims. Army rims are hard to find.

In my case, I am also upgrading the brakes on my MM540 to disk brakes so as part of the upgrade, I have to buy new front hubs so I decided to buy the scorpio hubs with the 160 PCD rims which will give me much more choices with rims. All newer Mahindra and Tata vehicles have 160 PCD rims.

Last edited by Rehaan : 18th April 2008 at 00:38. Reason: Merged. Please read about "quoting multiple posts" in the team-bhp FAQs.
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Old 17th April 2008, 03:39   #9
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Hi,

the only possible chance to have some good results, apart from modify the jeep to hold that size, body lift etc, to increase the resistance of all steering parts etc etc, is to reduce the ring and pinion ratios in yours differentials. With those tires, much bigger than original, to start the jeep your clutch will burn in few times, your speedo will never match the real speed and FE will be worse...
Go for Mud or All terrain, safer and better...
BTW, what is the precise size of what you have now?

Ciao

Ignazio
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Old 17th April 2008, 18:43   #10
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9-16 NDT tyres are available from MRF. But a proper conversion to larger dia tyres will require a lift job, track widening, final drive ratio reduction, brake upgadation, major steering modifications...
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Old 23rd April 2008, 10:13   #11
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Quote:
Originally Posted by Blue Thunder View Post
OT : have you got the tyre prices? and which brand?
Tire Prices
Apollo - Rs.5500/tire
Ceat - Rs.6000/tire
MRF also makes these tires. Yet to get the price.

Disc cost -
Rs.
4500/disc (new);
Rs.3000/disc(used)

Quote:
Originally Posted by Spitfire View Post
Why do you want to fit that tyre? I dont see much benefits.
My friend is planning on this. His farm is next to inaccessible during the rains. We need bigger tires. We have experienced CL500/500s with 15 inch radials, getting into a spin too soon. That is why we feel we need 7.00 x 16 or bigger. Here in Coimbatore we cannot get the 7.0x16 or 7.00 x 16 NDMS tires.
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Old 23rd April 2008, 10:14   #12
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Originally Posted by Sankar View Post
Also be wary about the speed rating of the JCB front tires. Some tires are not designed to go fast. JCB tire, based on it's application, i'm sure is not meant for highway speeds.
Good point. We never thought of this. The maximum we are planning to do on the jeep is about 65-70kmph.
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Old 23rd April 2008, 12:40   #13
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Quote:
Originally Posted by GTO View Post
I got 225's for my Jeep and wouldn't recommend anything wider than that. In fact, this size itself may be a little overkill for the kind of power (or lack of) that the diesels make.


My MM540 has 265/70 R16 on standard jeep rim. I have done close to 90 kmph on it, cornered well and had good ride quality too. Also did Keelambakkam quary route on these which is very unforgiving terrain. These were good on sand during my beach off roading

However i wouldnt recommend it to go for such large tyre. The following are the reasons-

1. Steering is very tight on city roads
2. During exterme articulation the tyres are rubbing inside the wheel wells

Infact iam planning to either go for 7.50 x16 MRF sand grips or use 7.00X16 standard tyre. May think of a radial with A/t pattern not exceeding 235 size.
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Old 23rd April 2008, 13:03   #14
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Quote:
Originally Posted by aandu
That is why we feel we need 7.00 x 16 or bigger. Here in Coimbatore we cannot get the 7.0x16 or 7.00 x 16 NDMS tires.
Jee, I believe 7.50x16 can be accomodated in the jeep rim.
And if u want them, we can help you source those tyres from Chennai.
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Old 23rd April 2008, 14:22   #15
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Quote:
Originally Posted by vinod_nookala View Post
2. During exterme articulation the tyres are rubbing inside the wheel wells
I suggest you add small spacers and disc brakes (disc brakes also work like spacers by bringing out the wheels a bit) to make sure the front tyres get the required clearance.
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