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[Ahnsahn]

Spoonman, on 2012-04-20 06:55:36, said:

Tanaka, the diameter difference between a 265/60/18 and a 265/50/20 is 0.27%, what is the momentum arm difference between them ?

Excellent question!!! (Pass the popcorn....) :-)

Tanaka, on 2012-04-19 17:45:13, said:

Ahnsahn, on 2012-04-18 19:31:25, said:

Notice any difference in the quality of ride comfort and handling between the 16" and the 18"? Which 18" tire brand did you install? Have you upgraded your shocks, too?

Getting technical, do you have any idea what kind of a performance difference there would be between your brake and tire upgrade on your DMax and on another DMax, installing 20" wheels, converting the rear brake drums to 320mm discs and installing larger 320mm discs on the front brakes (while keeping the OEM factory (2-pot?)? caliper)?

The ride comfort difference is a bit difficult to estimate as I changed the shocks as well and they are not as spongy as original but not rock hard racing units. But I do not feel the comfort being notably worse. And my rotors are 330mm ventilated. As was asked by someone putting larger rotors and keeping standard calipers does improve things. Up to a point, especially if you have two pot calipers. Putting big wheels like 20.s with original brakes is asking for trouble. Apart from low profile tyres on a pickup look silly, they are damned uncomfortable. And you need to look at the momentum arm for the brake. The distance from wheel centre to outer edge of the rotor and to that of  the tyre. Less difference in these measurements, better braking. In principle. There are other factors too but that is simple. Put larger wheels on with standard brakes and you have less effective braking.
Original tyres Bridgestone Dueler 16inch on the DMax are lethal in the wet. Literally. They are only a little better in the dry. But they are cheap for Isuzu. My present rubber is Japanese Nitto Dura Grappler H/T 265/60 18.
I would like to see a brake test between the two from 100kmh but Isuzu says they do not have that figure for the Bridgestones! I wonder why. I did not think to do this when I had the Bridgestones on and it is too late now. Another important thing regarding brakes is the pads. There is a big difference between different brake pads. I use EBC Green Stuff now and they seem to work nicely as I am not too hard on them.
Converting the rear drums to discs can be done for reasonable money but the question is why. Unless you intend to go racing or are often driving your truck hard on mountain roads, I see little advantage. The Isuzu is heavier on the front axle and that is increased when braking and thus taking more weight off the rear wheels making them prone to locking, which you do not want.

It took me a while  to discover, (Google), that you were referring to a physics principle(?) because with only my limited mechanical background to draw from, I couldn't conceptualize what you were describing. It's good to be privy of your knowledge in this area. So It is understood (and seconded by Spooman!) that adding larger 320mm rotors to the factory 2-pot calipers will at least provide noticeably more stopping power - though upgrading to 4-pot calipers would be even better.

I hear you about the rear brake conversion, that it wouldn't be as significant of a performance improvement as the front brake upgrade, but I'll also have the added peace of mind when going down some of those steep curvy mountain roads up north.

BTW, my upgrades are to a MU-7, a 'glorified' DMax. Though it's not 'The' DMax, If I get the chance, I can do a brake test with the 16" Dueler H/Ps before I install the new tires. I too, will have some (Gooru) shock absorbers installed.

I wrestled with 18" or 20" wheels, too. My initial decision was to go 18" because of my belief that 'generally', the more 'sidewall'(rubber) between the pavement and the wheel, the smoother the ride. The 18" tires had only 1/2" less sidewall than the 16" tires while the 20" tires have a whole 1-1/2" less sidewall than the 16" tires! But when I went tire shopping, all the dealers urged me not to go with the 18" but rather to go with the 20" wheels! If I do go with the 20's, I would only go with Yamaha Parada tires. For the 18", Bridgestone H/L Alenzas would be my first choice.

Edited by Ahnsahn, 2012-04-20 11:16:09.

[Tanaka]

Spoonman, on 2012-04-20 06:55:36, said:

Tanaka, the diameter difference between a 265/60/18 and a 265/50/20 is 0.27%, what is the momentum arm difference between them ?

Your point being? Did you read my post? I said bigger wheels with standard brakes gives less braking force and I described the difference in torque between the size of rotor and wheel,  not between 18 or 20 inch wheels.

[Ahnsahn]

Tanaka, on 2012-04-20 13:02:45, said:

Spoonman, on 2012-04-20 06:55:36, said:

Tanaka, the diameter difference between a 265/60/18 and a 265/50/20 is 0.27%, what is the momentum arm difference between them ?

Your point being? Did you read my post? I said bigger wheels with standard brakes gives less braking force and I described the difference in torque between the size of rotor and wheel,  not between 18 or 20 inch wheels.

I can't speak for Spoonman but I hope he wasn't being facetious or minimizing your, what, IMHO, was a very good topic explanation. I chimmed in on his question because I thought he was innocently asking whether you knew of some simple formula or numerical guide that can be used to match the correct sized rotors to 18" or 20" wheels.

Edited by Ahnsahn, 2012-04-20 13:43:12.

[Spoonman]

Tanaka, on 2012-04-20 13:02:45, said:

Spoonman, on 2012-04-20 06:55:36, said:

Tanaka, the diameter difference between a 265/60/18 and a 265/50/20 is 0.27%, what is the momentum arm difference between them ?

Your point being? Did you read my post? I said bigger wheels with standard brakes gives less braking force and I described the difference in torque between the size of rotor and wheel,  not between 18 or 20 inch wheels.

Yes I did read your post, You said many things but gave no real answers. my query between 18" and 20" rims is because you said one would need to upgrade brakes to run the larger rims due to the "momentum arm". I could calculate a smaller 20" tyre and most probably get it down to the same (or close to) rolling diameter as the stock tyre. but would the momentum arm still be the same ?


For what its worth yes I did upgrade my front brakes from OEM discs to 320mm ones due to the OEM being next to useless. Having said that when I had my wheels off for powerdercoating (before the disc upgrade) I had stock wheels/tyres on it, the brakes were just as bad then.

Edited by Spoonman, 2012-04-20 14:54:29.