Both the RLL-87-2 and the RLL-89-2 are extra long ramps. The 87" ramps are 10" high and the 89" ramps are only 8" high. The RLL-87-2 ramps have two distinct incline angles. The initial slope is 6.8˚. A little more than half way up the ramp, the incline changes to 10.7˚. Once the front tires are on the 6.8˚ incline section, the approach angle is effectively increased, so it's possible to increase the angle on the ramp. Increasing the angle part way up the ramp decreases the overall length of the ramp.
The RLL-89-2 progressive incline ramp has a curved top which gradually increases from 4˚ to 8˚. Using a curved top can reduce the length of the ramp by more than 25%. If your car required ramps with a 4˚ incline in order to reach the tires without hitting up against the spoiler, then constant slope ramps with a 4˚ incline would have to be 120" long in order to reach a platform that was 8" high. But since the RLL-89-2 ramps are curved, they get to 8" high with a length of only 89". The problem with the curved top ramps is that it's possible that they could fit up against the tires when the car is on the ground, but, scrape the car when it is part way up the ramps.
With a constant slope ramp, if the ramps can be pushed up against the tires when the car is on the ground, you are guaranteed that the car will clear the entire length of the incline section since the clearance between the ramp and the car increases as the car climbs the ramps. The easiest way to visualize this is to imagine a ramp that is longer than the wheelbase of the car. If a car with 4" of ground clearance has 1" of clearance when the tires are up against the starting edge of the ramps, there will be 4" of clearance between the car and the ramps once both axles are on the ramps.
The only way to guarantee adequate clearance the entire length of the progressive incline ramp would be to have a custom ramp for a given combination of wheelbase, overhang length, and ground clearance values. Since this is not really practical, the best I can do is verify whether or not a particular car can clear the entire length of the 89" ramps. Since a few customers had cars that would still scrape on the RLL-89-2 ramps, I also made an RLL-99-2 ramp with a total length of 99" and the same 8" height. The compromise with a 99" long ramp is that some cars with relatively short wheelbases give up the feature of being able to remove the inclines when the front tires are on the platform since the rear tires are on the inclines by the time the front tires reach the platform stop.
Some people may lament the fact that the RLL-89-2 ramps are only 8" high instead of 10" high. However, if your car requires the RLL-89-2 ramps for clearance in the front of the car, then it's very likely that if the rear tires were 10" off the ground, that the front bumper would be below the ground.
I doubt if you need the RLL-89-2 ramps for your GT-R unless it is lower than stock. Other forum members who purchased the RLL-87-2 ramps report that they have plenty of clearance with the two-stage incline ramps.
Socalaviator, on 14 February 2012 - 04:13 PM, said:
Thank you so much for all the info you have provided. I am currently looking at the RLL-89-2 since the extenders portion is already built in to one of the sections. (I'm assuming a Nissan GTR needs the extended portion to clear the ramp).
Other than overall length, what is the difference between the RLL-87-2 and the RLL-89-2?
I think I've narrowed my choices down.