[AbhiJ]

Happy Monday to all .


A purely academic question. I was just wondering, what are the adverse effects to increasing the diameter of one's tyre to a tyre with 105% diameter of the original?

Say..

Original Tyre : Diameter 600 mm
Upsize Tyre: Diameter 630 mm

For this hypothetical example, lets assume:

1) There is enough space in the wheel well so that even after complete suspension travel & full steering lock, the upsized tyres do NOT foul with the body.

2) The user does not mind the Speedo, Odometer error.

3) The upsized tyre weighs the same as the original tyre.

What might the long term effects be? Your inputs would be appreciated...

Mods: Made this thread in the Technical section because I believe the question has more to do with suspension rather than tyres..

[GTO]

What might the long term effects be? Your inputs would be appreciated..

I'm going to chip in here, as have been pondering over the same for my Jeep : Related Thread.

The effects of a larger diameter wheel + tyre combo:

1. Better ground clearance. However you need to ensure that the tyre doesn't scrape against your wheel arch.

2. Due to the higher stance, poorer handling & increased body roll.

3. Larger diameter = taller gearing = poorer acceleration, but (potentially) better top speed.

4. If the sidewall height has increased, better ride quality.

5. If larger diameter also means you widened the size of the patch, then more rolling resistance, lesser FE etc. Of course, you can maintain the same tyre width and still increase the diameter.

6. More weight : I don't buy your statement that they would weigh the same. Atleast if you stick to the same brand of wheel & tyre, logically, a smaller diameter would tip in the scales at a lower mark.

Then, there is the speedo error (which you mentioned), and possibility of messing up your car's ABS calibration.

[watashi75]

Some more points -

1. There will be an increase in FE due to the tall gearing
2. The tyre wear will be reduced because number of rotation will be less for the same mileage.
3. Ride will improve over smaller pot holes
4. Load carrying capacity will increase since suspension travel will increase

I think it will also affect the steering effort, but I am not sure in which way.

[Su-47]

Wont this have an impact on the engine longevity as well because of increased load? For high torque diesels this may not be much, but could be an issue for petrol-engines. Comments please...

Thanks,
Su-47

[UniqueMods]

Originally Posted by watashi75

Some more points -

1. There will be an increase in FE due to the tall gearing
2. The tyre wear will be reduced because number of rotation will be less for the same mileage.
3. Ride will improve over smaller pot holes
4. Load carrying capacity will increase since suspension travel will increase

I think it will also affect the steering effort, but I am not sure in which way.

i don't see how the suspension travel will increase. kindly explain.

UM

[watashi75]

Originally Posted by Su-47

Wont this have an impact on the engine longevity as well because of increased load?

What you are talking about is lugging the engine. Here is a nice discussion on lugging here -

http://www.team-bhp.com/forum/techni...ur-engine.html

There will be a decrease in torque at the wheels which will lead to lesser acceleration at any given RPM. But there won't be any impact on the engine longevity as long as you are not lugging the vehicle.

Originally Posted by UniqueMods

i don't see how the suspension travel will increase. kindly explain.

Sorry, I should have said "can" instead of "will increase". What I meant was that the vehicle will not bottom out.

[Shan2nu]

Wont this have an impact on the engine longevity as well because of increased load? For high torque diesels this may not be much, but could be an issue for petrol-engines. Comments please...

As long as you choose the right gears depending on engine speed and load, the engine wont feel bogged down.

Shan2nu

[nitrous]

Acceleration goes down!

[AbhiJ]

Originally Posted by GTO

More weight : I don't buy your statement that they would weigh the same.

Agreed. That is almost impossible. I just said that because I wanted to lessen one variable (Unsprung Weight etc)

Originally Posted by GTO

possibility of messing up your car's ABS calibration.

Ouch... that sounds scary!! Is that actually a risk?

[sgiitk]

Quite likely that the mix up in ABS will not be that bad. ABS runs on a closed loop and thus it should be able to adjust automatically to the new scenario.

[Trust_In_Thrust]

+1
ABS must not depend on the total diameter since this will always change .A new tyre will be having a bigger diameter compared to a old worn out one.So ABS should not be affected by change in tyre sizes.

[Rehaan]

Originally Posted by AbhiJ

....A purely academic question. I was just wondering, what are the adverse effects to increasing the diameter of one's tyre to a tyre with 105% diameter of the original?
.....

To add to the fairly extensive list of changes already mentioned :

Steering response will be a little less sharp. ie there will be more sidewall, and therefore when you turn your wheel there is more rubber to flex, which equals a less direct and quick response. This is the reason why low-profile tyres have better/quicker steering response.
(Think of it like moving a paintbrush against a paper - the handle is the metal rim, and the brush hairs are the flexible sidewall. The longer the hairs, the more sloppy the painting control.)

Also, when cornering, your car will be less likely to "hold the line" as well, for the same reason as above - more sidewall = the more your car will deviate sideways.

Illustration:


Also, the higher profile tyres may make your car seem a little less straight-line solid during braking (due to more flexing in the sidewall causing some side to side motions).

EDIT: heres a thread that pretty much asks your question "high profile vs low profile!"
http://www.team-bhp.com/forum/tyre-a...ile-tyres.html

Originally Posted by AbhiJ

....Mods: Made this thread in the Technical section because I believe the question has more to do with suspension rather than tyres..

Has little to do with suspension though.

Originally Posted by watashi75

....
Sorry, I should have said "can" instead of "will increase". What I meant was that the vehicle will not bottom out.

This has been covered under "Ground Clearance will increase" and doesn't really have anything to do with the suspension in this example.

Originally Posted by AbhiJ

Agreed. That is almost impossible. I just said that because I wanted to lessen one variable (Unsprung Weight etc)

Well its definitely not impossible if you go from one brand/model tyre to a larger tyre of a different brand/model. It could definitely end up being lighter.

Also, add to that if you do change alloys as well - could be an even larger weight saving!

Originally Posted by sgiitk

Quite likely that the mix up in ABS will not be that bad. ABS runs on a closed loop and thus it should be able to adjust automatically to the new scenario.

Originally Posted by Trust_In_Thrust

+1
ABS must not depend on the total diameter since this will always change .A new tyre will be having a bigger diameter compared to a old worn out one.So ABS should not be affected by change in tyre sizes.

In this example the effects are negligible, however, there will probably be some effect - it wont be exactly the same if you think about it.

cya
R

[humyum]

Ok i have first hand experience in this as i had an 800 with 145/80/R12 against the 145/70/R12

A profile increase of 10, and it did not foul with te wheel wells even under full load but it could vary from vehicle to vehicle.

Mine was a carburated 800. The acceleration did go down a tad bit but since a carburated 800 has better low down torque as compared to the mpfi 6 valved ones so it was not bad. Yes body roll was a tad more and so the handling of the car too was a tad less as compared to the 70 profile tyres.

Advantage although was better mileage, ground increased too so no scraping any speedbreakers and the ride quality was cusion, small undulation went unnoticed and way better tahn the 70 profile tyres.Top speed i am not sure, Mine used to touch a speedo indicated 130 kmph.

And yes as Rehaan said it does hold less of a line while cornering.

[Sprucegoose]

Hypothetically, [I don't intend to do this]
I have an OHC. If i upsize my tyre size by getting lets say 205/50R16 [rather than 205/50R15] rubber, then the tyre is bigger than the stock 175/70R13, but still has a smaller side wall.

This way we have won't get degraded handling. or a ride thats too bumpy.

[AbhiJ]

Originally Posted by Sprucegoose

Hypothetically, [I don't intend to do this]
I have an OHC. If i upsize my tyre size by getting lets say 205/50R16 [rather than 205/50R15] rubber, then the tyre is bigger than the stock 175/70R13, but still has a smaller side wall.

This way we have won't get degraded handling. or a ride thats too bumpy.

If you get 205/50 R 15 or 205/50 R 16, the sidewall height remains the same.

The handling / ride should not change much, if at all.