215/40R21 vs 235/35R21
Going from one to the other changes the overall height by -1.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/40R21 | 235/35R21 | Change |
|---|---|---|---|
| Overall height | 27.8" | 27.5" | -1.1 % |
| Sidewall | 3.39" | 3.24" | -4.4 % |
| Section width | 215 mm | 235 mm | +9.3 % |
| Circumference | 87.2" | 86.3" | -1.1 % |
| Revs per mile | 726 | 734 | +1.1 % |
| Axle height | 13.89" | 13.74" | -3.8 mm |
| Approved rim width | 6–8" | 6.5–8.5" | overlap 6.5–8" |
Both are approved on a rim 6.5" to 8" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 215/40R21. Fit 235/35R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.5 mph | -0.5 |
| 70 mph | 69.3 mph | -0.7 |
| 90 mph | 89.0 mph | -1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,894 on the road, so it over-counts by 106. At a true 70 mph the first turns 847 times a minute, the second 856.