Comparing Progress and Racing Beat Springs by BestCS

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A Comparison of Progress and Racing Beat Springs using Tokico HTS Shocks

The purpose of this post is to compare my results of using Progress springs and Racing Beat springs using Tokico HTS shocks, Fat Cat Motor Sports (FCM) bumpstops, and stock sway bars. The victim was an '06 MX-5 soft top with stock 17" wheels and 215/45 rubber. The following is data collected for the stock, RB, & Progress springs:

Spring Rates F/R

Stock: 116/90

RB: 145/112

Progress: 126/116

Wire Diameter F/R

Stock: 0.421875/0.390625

RB: 0.453125/0.421875

Progress: 0.437500/0.40625

Free Length F/R

Stock: 15.50/14.0

RB: 13.25/12.25

Progress: 13.50/13.0

Number of Coils F/R

Stock: 7/7 

RB: 9/8

Progress: 7/9

The RB spring has been a popular option for lowering the MX-5 a modest amount around 0.5" but has received some bad press for sagging in the rear when used on PRHT (Power Retractable Hard Top). However, Racing Beat has warned that the spring should only be used on the soft top. I take this to mean the RB spring was designed specifically for the soft top. Recently, another spring from the Progress Auto Group has come on the market. This spring was part of a package developed by Mazda called the MS-R ( Motor Sport Racing). 

I have installed and tested both springs on my MX-5. The RB springs did exactly as advertised lowering the car exactly 0.5" front and back. RB recommended altering the stock bumpstops, but I replaced them with a set from FCM. I set the damping of the HTS shock Front/Back 3/4 turns (counter clockwise) from full hard. From a cosmetic perspective the car looked good and the ride although firm was still comfortable even over the worst patches of roadway. Finally, the car had a nice rake of about 0.25" (front lower than the back).

Next I installed the Progress springs. After dropping the car to the ground with the suspension bolts loose, I got an unpleasant surprise. The front dropped at least 0.5" maybe a bit more, and the back was at the stock ride height or slightly higher - perhaps a quarter inch! I took the car out for a ride to see if the ride height would change, but it didn't. I tightened up the suspension bolts and adjusted the damping on the shocks to F/R 4/4. Over the next week, I tried various settings but couldn't get anything I liked. At all settings, the ride felt lumpy, hard, and just plain uncomfortable. I ended up leaving it at F/R 4/4. Cosmetically the Progress springs looked terrible. The back end was just too high exposing a huge gap between the tire and the lip of the fender. With the modest drop in the front and the high rear end, the car looked jacked up in the rear with too much rake. Frankly I consider the Progress springs a poorly designed product not worth considering for the MX-5 soft top.

Unfortunately, besides the stock spring, there isn't an aftermarket spring that will properly work on both versions of the MX-5, i.e., the soft top and PRHT. What Progress has attempted to do is design one that will work on both. If you look at the above specifications, the Progress rear is taller than the RB with more coils than either the stock or the RB. When used on the soft top, you'll get my results. I'm guessing that the rear spring might be OK for the PRHT, but the front may still be two low for your tastes. 

Finally. Progress says the amount of lowering is dependent upon the shock used. What sort of mumble jumbo is that? The ride height of my car is exactly the same using the stock springs with either the Yellow Bilsteins (part of the Sports Package) or the HTS. So the company is saying that to properly lower the car front and back a nominal amount one must use some special shock? I sent Progress a letter about this situation, but they have refused to respond.

Anyway, the RB springs have worked out well on my car, and I plan on keeping them.

BestCS