Tire Diameter and ride height question

[Jferrante]

All right everyone please pardon my ignorance here but I have what I believe is a potentially stupid question...
I am currently running 275-60-15 all around on my 64 C10 with airbags. My front tires rub wayyy to much on full turn when the truck is lowered (i actuallly popped one) so I am thinking of going to a 225-60-15 up front which would be ~2" less in total diameter.
My question is, will the smaller tire lower my front ride height by the ~2"? If so will this have a similar effect a rear lowering block has -allowing me to run higher psi in the front bags at a lower height to improve ride quality???
Is my logic sound or am I completely off?
Thanks again

[Tazimafied]

You have a dilemma with width as well. Your current tire is almost 11 inches wide. The tire you want to change to is almost 9 inches wide. Would your wheel support the smaller width without looking odd?

As far as the diameter goes you will loose 2 inches in diameter but only one inch in the radius which is the measurement from the center of the wheel to the tread. That means you only loose half the diameter in ride height.

[Jferrante]

I am going to new rims - 15 x7 up front and continuing 15x8 in the back - but makes sense the decrease in diameter divided by 2 will give me my adjusted ride height.

[Tazimafied]

Sounds like you are pretty well set with the new size then. Decreasing the diameter and width will increase your clearance drastically.

[Jferrante]

Originally Posted by Tazimafied

Sounds like you are pretty well set with the new size then. Decreasing the diameter and width will increase your clearance drastically.

Thanks for the reply and confirmation!

[vin63]

Originally Posted by Jferrante

All right everyone please pardon my ignorance here but I have what I believe is a potentially stupid question...
I am currently running 275-60-15 all around on my 64 C10 with airbags. My front tires rub wayyy to much on full turn when the truck is lowered (i actuallly popped one) so I am thinking of going to a 225-60-15 up front which would be ~2" less in total diameter.
My question is, will the smaller tire lower my front ride height by the ~2"? If so will this have a similar effect a rear lowering block has -allowing me to run higher psi in the front bags at a lower height to improve ride quality???
Is my logic sound or am I completely off?
Thanks again

The diameters are 275-60R15 - 28.1"; for the 225-60R15 - 25.6"

[Clyde65]

I am running a 4/5 drop with 15x8\275/60/15 rear and 15x7\215/70/15 in front. tire size is 27/28 front and rear. I dont rub, even on turns or inclines. one note, I dont have bags on front so I am at same height at all times.

Hope this helps!

[Free Candy Inside]

I'm going to run 205/75/15s on the front and 215/75/15s on the rear of my Paneltruck because Im bagged and channeled so it lays door. I get full turn lock to lock even layed out. Now that's without a hood on. Might hit the hood when layd out

[Jferrante]

Originally Posted by Clyde65

I am running a 4/5 drop with 15x8\275/60/15 rear and 15x7\215/70/15 in front. tire size is 27/28 front and rear. I dont rub, even on turns or inclines. one note, I dont have bags on front so I am at same height at all times.

Hope this helps!

Thanks, yea I am only rubbing when I am almost fully bagged out (not laying frame)

[Jferrante]

Originally Posted by Free Candy Inside

I'm going to run 205/75/15s on the front and 215/75/15s on the rear of my Paneltruck because Im bagged and channeled so it lays door. I get full turn lock to lock even layed out. Now that's without a hood on. Might hit the hood when layd out

First off love your build - I am not laying frame but when I am fully deflated I hit the LCA's I believe and one of them had a sharp piece that cut one of my tires. I might take the angle grinder to it this weekend.

[62step]

This helped me out a lot, shows you the different tire sizes side by side.

http://tire-size-conversion.com/tire-size-comparison/

[joedoh]

Originally Posted by Jferrante

allowing me to run higher psi in the front bags at a lower height to improve ride quality???

a better ride comes from lower pressure. pressure is directly related to spring rate, the higher the pressure the higher the spring rate. if you have ever owned or ridden in a 3/4 ton truck, you know that the unloaded ride is terrible, and that the loaded ride is much better. this is because of the high spring rate, "it rides like a lumber wagon".

do you have shocks? the number one mistake people make when bagging a truck is not installing shocks. an air spring is there to absorb uneven road surface and bumps, just like a steel coil or leaf spring, but all springs oscillate to get rid of that energy, the oscillation is newtons third law in practice where the spring compresses, then uncompresses an equal amount minus the friction and other losses. this gives the poor ride some people have with airbags. a shock is there to dampen the oscillation and return the spring to a neutral position faster, by turning the compression/rebound energy to heat (conservation of energy). without shocks, the TIRE is what takes up the oscillation and even if it feels ok inside to watch the tire from outside is a real show, it bounces and jitters and stretches and all sorts of other adjectives.

if you have shocks, you might have the wrong ones. I recommend as large a shock as fits and gas charged, rebuilding the mounts if needed, because there is a lot of energy in throwing that big mass of the front end and engine up and down. smaller shocks will foam, and the air in the fluid renders the shock useless after a few miles.

here is a picture of the shock I used on my truck, compressed length is 12" and it has 8" of travel, gas charged. When I am driving even at 2" off the ground the truck just MELTS down the road. it is an offroad shock, meaning it has more rebound than compression resistance, and that works well on an airspring.


oh and one other thing, I think you meant that you would have higher pressure because the truck would bottom out before the airspring was fully collasped. if that is what you meant, yes, you will need more pressure to lift because the spring is just building pressure without lifting for a few seconds. this is not a great thing though, detailed above in the changes to your ride, usually you want the spring to compress fully right at the point the truck hits the ground. If thats not what you meant, maybe you meant you would get an extra inch of drop with smaller tires, I will say that will be true only if the truck did not hit the ground before.

good luck!

[Jferrante]

Originally Posted by joedoh

a better ride comes from lower pressure. pressure is directly related to spring rate, the higher the pressure the higher the spring rate. if you have ever owned or ridden in a 3/4 ton truck, you know that the unloaded ride is terrible, and that the loaded ride is much better. this is because of the high spring rate, "it rides like a lumber wagon".

do you have shocks? the number one mistake people make when bagging a truck is not installing shocks. an air spring is there to absorb uneven road surface and bumps, just like a steel coil or leaf spring, but all springs oscillate to get rid of that energy, the oscillation is newtons third law in practice where the spring compresses, then uncompresses an equal amount minus the friction and other losses. this gives the poor ride some people have with airbags. a shock is there to dampen the oscillation and return the spring to a neutral position faster, by turning the compression/rebound energy to heat (conservation of energy). without shocks, the TIRE is what takes up the oscillation and even if it feels ok inside to watch the tire from outside is a real show, it bounces and jitters and stretches and all sorts of other adjectives.

if you have shocks, you might have the wrong ones. I recommend as large a shock as fits and gas charged, rebuilding the mounts if needed, because there is a lot of energy in throwing that big mass of the front end and engine up and down. smaller shocks will foam, and the air in the fluid renders the shock useless after a few miles.

here is a picture of the shock I used on my truck, compressed length is 12" and it has 8" of travel, gas charged. When I am driving even at 2" off the ground the truck just MELTS down the road. it is an offroad shock, meaning it has more rebound than compression resistance, and that works well on an airspring.


oh and one other thing, I think you meant that you would have higher pressure because the truck would bottom out before the airspring was fully collasped. if that is what you meant, yes, you will need more pressure to lift because the spring is just building pressure without lifting for a few seconds. this is not a great thing though, detailed above in the changes to your ride, usually you want the spring to compress fully right at the point the truck hits the ground. If thats not what you meant, maybe you meant you would get an extra inch of drop with smaller tires, I will say that will be true only if the truck did not hit the ground before.

good luck!

thanks for the detailed response. I do have shocks and just changed them to the KYB drop shocks - but when I am slammed it still rides rough since the shocks are essentially useless then.

I was comparing psi to the effect that lowering blocks have on the rear.

[Palf70Step]

I run 15x8 wheels with a 245/60x15 on my front. 4.5" drop 275/60x15 on 15x8 wheels on 6' rear drop. No rubbing issues at all

[Jferrante]

truck looks great! and thank you I will be going with 225 or 245 60

[joedoh]

Originally Posted by Jferrante

I was comparing psi to the effect that lowering blocks have on the rear.

ahh gotcha. lowering blocks raise the axle centerline in relation to the suspension, so a smaller tire wont have the same effect. To get the same effect, you would need drop spindles (assuming you didnt already have them) or lowered lower control arms to raise the axle centerline.

[Jferrante]

ended up going with 225-70-15 which is basically the same circumference and just ordered front shock relocators to help smooth the ride when being aired out - the 225 will allow more clearance as well...thanks for all the help

[Tazimafied]

Pic?

[Jferrante]

Originally Posted by Tazimafied

Pic?

everything is en route - next week should be pics

[Jferrante]

Here they are mounted and dirty as hell since NJ roads are made of salt- I am fully aired out here with 2" drop blocks in the rear - this pic makes me want to go lower

[61_FL_Apache]

If you want to look at my build, im running 235/60/15 on the front and 255/70/15 on the rear. All are 8" wide and the rear is bagged.